The present invention relates to a fuel injection system for an internal combustion engine.
A particularly effective method for reducing the toxic components in the exhaust gas of an internal combustion engine consists in recycling specific quantities of exhaust gas according to the particular operating state of the engine. A reduction in the amount of nitrogen oxide in the exhaust gas is achieved by means of this method. However, as this reduction in the nitrogen oxides in the exhaust gas is known to be accompanied by an increase in the amounts of soot, CO and HC in the exhaust gas, it is necessary to strictly regulate the exhaust gas recycling rate, the quantity of fresh air supplied and the quantity of fuel injected so as to obtain an optimum air excess over the entire load range of the engine. At low speeds, and particularly during idling, the performance of the engine is adversely affected by excessive exhaust gas recycling rates.
One fuel injection system proposing exhaust gas recycling is disclosed in German OS (laid open patent application) No. 2,321,970. This patent application describes a fuel injection system for diesel engines wherein an exhaust gas quantity which has been adapted to the quantities of fuel injection or to the particular engine load which has been engaged, is recycling to the suction side of the engine. In this case, a specific fuel-air mixture can be supplied to the engine in that the fresh air which is sucked in and the quantity of fuel injection are constantly regulated in dependence on one another by means of an air metering device and a fuel metering device. A reduction in the NO.sub.x components in the exhaust gas is obtained by regulated exhaust gas recycling.
Another proposed system includes a suction tube and a throttle valve disposed in the suction tube upstream of the mouth of an exhaust gas recycling line discharging into the suction pipe for controlling the exhaust gas return flow. Also included are an air metering element measuring the quantity of fresh air drawn into the suction tube and a fuel injection device whose arbitrarily variable delivery constitutes a reference parameter for a regulating device controlling the throttle valve by means of a hydraulic servomotor. The fuel suction line of the injection device contains an uncontrolled pressure chamber of a differential pressure valve and upstream thereof a throttle cross-section which is variable by means of a control plunger displaceable by means of the air metering element in opposition to a regulatable essentially constant hydraulic restoring force. The controlled outflow opening of the pressure chamber of the differential pressure valve, which is exposed to a substantially constant reference pressure, is in communication with the working chamber of the servomotor.